CVE-2026-107573: Incorrect Default Permissions in hMailServer
Incorrect default permissions in the Windows installer of Progressive Robot hMailServer 6.0.0 through 6.3.5 allow a local authenticated user to read the mail server's data. The installer created the data, log, temp, database and event folders and the hMailServer.INI configuration file with the permissions inherited from the installation folder, by default under Program Files, which give the local Users group read access. Any user who can sign in to the computer could read every stored message, the logs, the built-in database with the accounts' password hashes whenever the service is stopped, and the configuration file, including the database password, which is sealed only with the machine's DPAPI key and can be unsealed by any local account; with an external database that password gives full control of it. The Linux AppImage of 6.3.0 through 6.3.5 likewise created its per-user data folders readable by other local users.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
hMailServerto a version that resolves this vulnerability.Fixed in 6.3.6 - Configuration
From an elevated prompt, remove the inherited entries for Users and the application package groups using icacls with /inheritance:d, then /remove:g.
hMailServer data, log, temp, database, and event folders plus hMailServer.INI Windows filesystem permissions = Remove inherited Users and application package group entries - Operational
Change the database password and the administrator password if accounts that are not administrators could sign in to the server.
Event History
Frequently Asked Questions
Which installations are exposed by the insecure defaults?
Windows installations made with the installer in versions 6.0.0 through 6.3.5 are affected when the created folders and hMailServer.INI retain the inherited permissions. Linux AppImage installations in versions 6.3.0 through 6.3.5 are also affected because per-user data folders can be readable by other local users.
What access does an attacker need?
An attacker needs only an authenticated local account on the host. No interaction with the mail server is required; any user able to sign in to the computer may be able to read the exposed files.
What information can a local user obtain?
A local user may read stored messages, logs, temporary data, the configuration file, and the built-in database when the service is stopped, including account password hashes. The database password in the configuration can be unsealed by any local account using the machine's DPAPI key; for an external database, that password provides full control of the database.
How can I determine whether an existing installation is affected?
Check whether the hMailServer data, log, temp, database, and event folders and hMailServer.INI are readable by the local Users group on Windows. For Linux AppImage deployments, check whether other local users can read the AppImage-created per-user data folders.